1. Field of the Invention
The present invention relates to a semiconductor light-emitting device such as a light-emitting diode (LED), and more particularly to a method for manufacturing a semiconductor light-emitting device including a step in which the growth substrate used for crystal growth of the semiconductor film is removed using a laser lift-off method.
2. Description of the Related Art
Recent advances in technology have increased the efficiency and output of light-emitting elements such as light-emitting diodes (LEDs). However, the amount of heat generated by these light-emitting elements has risen along with output, and this heat has made them less reliable. In order to solve this problem, the growth substrate, which has relatively low thermal conductivity, has been removed, and replaced by a metal with relatively high thermal conductivity to support the semiconductor film. In addition to improving the heat radiating properties of the light-emitting element, the removal of the growth substrate in this configuration can be expected to improve light emission efficiency and the light extraction efficiency in particular. In other words, the light absorption that occurs when light passes through the growth substrate, and the light components completely reflected at the interface between the semiconductor film and the growth substrate due to the difference in refractive indices can be reduced. When a growth substrate of GaN-based semiconductor film is delaminated, the laser lift-off (LLO) method is most commonly used.
A technique is described in Japanese Patent Kokai No. 2003-303994 (Patent Literature 1) in which carbon-based foreign matter caused by the resin material near the semiconductor film adheres to the peeling surface of the semiconductor film during laser lift-off, and the foreign matter is removed by the laser.
The following procedure is disclosed in Japanese Patent Kokai No. 2002-261032 (Patent Literature 2) as a method for removing the growth substrate without using the laser lift-off method. A periodically stripe-shaped or island-shaped sacrificial film is formed on the surface of a sapphire substrate. A first nitride semiconductor is grown in the lateral direction from the exposed portion of the sapphire substrate, and growth is stopped by the lack of sacrificial film cover. The sacrificial film is then removed using etching to form a space in the lower portion of the first nitride semiconductor. A second nitride semiconductor is grown on the upper surface of the first nitride semiconductor and the side surfaces or the growth portion extending in the lateral direction. This forms space inside the nitride semiconductors, and the nitride semiconductors are supported by a column-shaped structure on top of the sapphire substrate. Because the joining strength between the nitride semiconductors and the sapphire substrate has been reduced, the sapphire substrate can be removed by vibrations or a thermal shock.
When a Cu film, for example, is formed on the surface of the semiconductor film as a support substrate, lattice-shaped element-dividing grooves (streets) are formed along the element dividing lines demarcating the first section of the semiconductor light-emitting device on the semiconductor film, and the surface of the semiconductor film is smoothed by the embedding of resin in these element-dividing grooves. The Cu film is formed on top of the smoothed semiconductor film using electroplating or another technique. Afterwards, the growth substrate is removed using the laser lift-off method. In such a resin-embedded semiconductor light-emitting device, the following problem occurs when the growth substrate is delaminated using the laser lift-off method. In the laser lift-off method, a laser is directed at the growth substrate from the rear surface, and the GaN-based semiconductor film formed on top of the growth substrate breaks down into metallic Ga and N2 gas. It is difficult to discharge the N2 gas at this time, and so it collects near the interface between the semiconductor film and the growth substrate. The impact from the N2 gas pressure sometimes causes the semiconductor film to crack. Exposure to the laser beam causes simultaneous breakdown and evaporation of both the semiconductor film and the resin, and some of the resin is likely to remain in the portions adjacent to the semiconductor film. When the growth substrate is delaminated with resin remaining on the perimeter of the semiconductor film, the edges and corners of the semiconductor film sometimes becomes cracked. Also, because exposure to the laser beam causes simultaneous breakdown and evaporation of both the semiconductor film and the resin, carbon-based materials generated by the resin material due to laser exposure is introduced below the surface of the semiconductor film exposed by the peeling off of the growth substrate, and the carbon-based foreign matter adheres to the exposed surface of the semiconductor film. Afterward, when electrodes and other elements are formed on the exposed surface of the semiconductor film and processing is performed to improve the light extraction efficiency, the steps described in Patent Literature 1 are required to remove the carbon-based foreign matter adhering to the surface of the semiconductor film.
In the technique described in Patent Literature 2, the growth substrate can be delaminated from the semiconductor film without using the laser lift-off method. However, crystal growth of the semiconductor substrate is a complicated process performed in two stages with a sacrificial film etching stage interposed between them. Also, when etching is used as the method for removing the sacrificial film, damage sometimes occurs to the electrodes and insulating film formed on the surface of the semiconductor film.